Organism discovered that has remained unchanged for more than 2 billion years

A section of a 2.3 billion-year-old rock bearing fossils (the dark areas) that are essentially identical to ones that are 500 million years younger, and to modern microorganisms that live in seawater mud (Photo: J. William Schopf/UCLA Center for the Study of Evolution and the Origin of Life)

Claimed to be the greatest lack of evolution ever discovered, a deep-sea microorganism – sulfur bacteria – recently uncovered by an international group of scientists is reported not to have evolved for more than 2 billion years. Despite it appearing to be an aberration in nature, researchers say that the microscopic creature’s unchanging nature actually supports Charles Darwin’s theory of evolution.

Dating back to a period in Earth’s history between 2.2 billion and 2.4 billion years ago known as the Great Oxidation Event (GOE), microorganisms such as the studied sulfur bacteria began to appear. The oxygen rise in the GOE had been produced by cyanobacteria over the 200 million years previous when oxygen production was so copious that it could no longer be chemically contained in sinks like dissolved iron or organic compounds, and it accumulated in heavy concentrations in the atmosphere. This event was also accompanied by an equally intense increase in sulfate and nitrate – essential nutrients for bacteria – and, as a result, the bacteria were able to flourish and reproduce in enormous numbers.

Skip forward some 2 billion-odd years, and scientists looking at similar fossilized sulfur bacteria in rocks off the Western Australian coast, noted that those which were 1.8 billion years old were exactly the same in every way to those which had existed 2.3 billion years ago. Whilst this was considered unusual, it was not until recently – when other scientists discovered that both these sets of microorganism fossils were also completely indistinguishable from the same sulfur bacteria that exist today off the coast of Chile – that the penny dropped about how unusual this actually was. The microorganism had not changed in any way for over 2 billion years.

"It seems astounding that life has not evolved for more than 2 billion years – nearly half the history of the Earth," said Professor J. William Schopf, director of UCLA’s Center for the Study of Evolution and the Origin of Life. "Given that evolution is a fact, this lack of evolution needs to be explained."

Darwinian concepts of evolution are largely premised on the observed changes in species whose attributes mutate over time to fit with changes in their environment. As such, any organisms whose characteristics alter in successive generations in ways that allow them to better adapt to altering living conditions are the ones who best suit their environment and are best able to carry on their evolutionary line.

To some this lack of change over 2 billion years may seem contradictory to Darwinian evolution. However, this behavior is actually in keeping with it. The scientists themselves explained that the environment in which these microorganisms live has remained essentially unchanged for 3 billion years.

"The rule of biology is not to evolve unless the physical or biological environment changes, which is consistent with Darwin. These microorganisms are well-adapted to their simple, very stable physical and biological environment," said Professor Schopf. "If they were in an environment that did not change but they nevertheless evolved, that would have shown that our understanding of Darwinian evolution was seriously flawed. It fits perfectly with his (Darwin’s) ideas."

Despite a common misconception regarding the term "survival of the fittest", Darwinian evolution does not necessarily mean that the strongest or toughest survive. Darwin used that statement to mean those creatures that were of the best fit, as in "fit for purpose" in their environment, not necessarily the ones that could fly the highest or run the fastest. The ancient sulfur bacteria are a perfect example of this – they simply were best suited to their environment and as their environment didn't alter they also didn't need to evolve to survive.

To thoroughly analyze the fossils, Professor Schopf employed a number of techniques including Raman spectroscopy – where information about molecular vibrations induced through electromagnetic excitation (generally with a laser beam) is analyzed and used for sample identification of composition and chemistry – along with confocal laser scanning microscopy, which has an ability to acquire in-focus images from selected depths. In other words, in "3D".

Professor Schopf is credited with pioneering the use of these techniques in the analysis of microscopic fossils sealed within primeval rocks.

The multinational team included researchers and scientists from UCLA, the University of Wisconsin, NASA’s Jet Propulsion Laboratory, the University of New South Wales, Australia, and the Universidad de Concepción in Chile. Their findings were published in the journal Proceedings of the National Academy of Sciences.

1.8 billion year old fossilized bacteria preserved in rock (Photo: J. William Schopf/UCLA Center for the Study of Evolution and the Origin of Life)

Scientists say that a type of deep-sea microorganism has not evolved in more than 2 billion years (Image: J. William Schopf/UCLA Center for the Study of Evolution and the Origin of Life)

A section of a 2.3 billion-year-old rock bearing fossils (the dark areas) that are essentially identical to ones that are 500 million years younger, and to modern microorganisms that live in seawater mud (Photo: J. William Schopf/UCLA Center for the Study of Evolution and the Origin of Life)